This is Not a Tree
Dreaming of a Bright Christmas

How long is a day?

Sunset in Buckinghamshire

We all know how horrible and dark it is, this time of year. But it’s not all bad. The earliest sunset has already come and gone, and the evenings have slowly been getting lighter for several days, even though the days have been getting shorter.

Today is the Winter Solstice, the shortest day of the year.

From today, the sunrise will continue to get later until two or three days into the New Year, then the morning will start to get lighter. At last.

This little discrepancy with the shortest day and the sunrise and sunset times is due to the Earth’s orbit being elliptical rather than perfectly circular, so that a solar day (measured from the point where the sun is highest in the sky each day) isn’t always the same length and doesn’t always match up with the 24 hour clock.

Around the Summer and Winter solstices the solar day is over 24 hours, then at the Spring and Autumn Equinoxes, the solar day is less than 24 hours. But it all evens out in the end. The axial tilt of the Earth also makes a difference.

One month from now, the day will be over 51 minutes longer, and the sunset will be 38 minutes later. On the Summer Solstice, we will be getting over nine hours more daylight, a total of sixteen and three quarter hours. I can’t wait.

About 70 miles to our North, (and quite a few miles East) is Cromer, on the North Norfolk coast. On the Summer Solstice they’ll get a day that’s over eleven minutes longer than we get here. Those few miles North make a difference, but of course at this time of year they get shorter days instead.

Okay, great. Like every year, tomorrow we start the long slow climb into Summer. Meanwhile, for readers in the Southern hemisphere this will all make sense in just six months time…

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